package com.singleman.okio;
/*
 * Copyright (C) 2014 Square, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.charset.Charset;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import static com.singleman.okio.Util.checkOffsetAndCount;
import static com.singleman.okio.Util.reverseBytesLong;

/**
 * A collection of bytes in memory.
 *
 * <p><strong>Moving data from one buffer to another is fast.</strong> Instead
 * of copying bytes from one place in memory to another, this class just changes
 * ownership of the underlying byte arrays.
 *
 * <p><strong>This buffer grows with your data.</strong> Just like ArrayList,
 * each buffer starts small. It consumes only the memory it needs to.
 *
 * <p><strong>This buffer pools its byte arrays.</strong> When you allocate a
 * byte array in Java, the runtime must zero-fill the requested array before
 * returning it to you. Even if you're going to write over that space anyway.
 * This class avoids zero-fill and GC churn by pooling byte arrays.
 */
public final class Buffer implements BufferedSource, BufferedSink, Cloneable {
    private static final byte[] DIGITS =
            { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };
    static final int REPLACEMENT_CHARACTER = '\ufffd';

    Segment head;
    long size;

    public Buffer() {
    }

    /** Returns the number of bytes currently in this buffer. */
    public long size() {
        return size;
    }

    @Override public Buffer buffer() {
        return this;
    }

    @Override public OutputStream outputStream() {
        return new OutputStream() {
            @Override public void write(int b) {
                writeByte((byte) b);
            }

            @Override public void write(byte[] data, int offset, int byteCount) {
                Buffer.this.write(data, offset, byteCount);
            }

            @Override public void flush() {
            }

            @Override public void close() {
            }

            @Override public String toString() {
                return Buffer.this + ".outputStream()";
            }
        };
    }

    @Override public Buffer emitCompleteSegments() {
        return this; // Nowhere to emit to!
    }

    @Override public BufferedSink emit() {
        return this; // Nowhere to emit to!
    }

    @Override public boolean exhausted() {
        return size == 0;
    }

    @Override public void require(long byteCount) throws EOFException {
        if (size < byteCount) throw new EOFException();
    }

    @Override public boolean request(long byteCount) {
        return size >= byteCount;
    }

    @Override public InputStream inputStream() {
        return new InputStream() {
            @Override public int read() {
                if (size > 0) return readByte() & 0xff;
                return -1;
            }

            @Override public int read(byte[] sink, int offset, int byteCount) {
                return Buffer.this.read(sink, offset, byteCount);
            }

            @Override public int available() {
                return (int) Math.min(size, Integer.MAX_VALUE);
            }

            @Override public void close() {
            }

            @Override public String toString() {
                return Buffer.this + ".inputStream()";
            }
        };
    }

    /** Copy the contents of this to {@code out}. */
    public Buffer copyTo(OutputStream out) throws IOException {
        return copyTo(out, 0, size);
    }

    /**
     * Copy {@code byteCount} bytes from this, starting at {@code offset}, to
     * {@code out}.
     */
    public Buffer copyTo(OutputStream out, long offset, long byteCount) throws IOException {
        if (out == null) throw new IllegalArgumentException("out == null");
        checkOffsetAndCount(size, offset, byteCount);
        if (byteCount == 0) return this;

        // Skip segments that we aren't copying from.
        Segment s = head;
        for (; offset >= (s.limit - s.pos); s = s.next) {
            offset -= (s.limit - s.pos);
        }

        // Copy from one segment at a time.
        for (; byteCount > 0; s = s.next) {
            int pos = (int) (s.pos + offset);
            int toCopy = (int) Math.min(s.limit - pos, byteCount);
            out.write(s.data, pos, toCopy);
            byteCount -= toCopy;
            offset = 0;
        }

        return this;
    }

    /** Copy {@code byteCount} bytes from this, starting at {@code offset}, to {@code out}. */
    public Buffer copyTo(Buffer out, long offset, long byteCount) {
        if (out == null) throw new IllegalArgumentException("out == null");
        checkOffsetAndCount(size, offset, byteCount);
        if (byteCount == 0) return this;

        out.size += byteCount;

        // Skip segments that we aren't copying from.
        Segment s = head;
        for (; offset >= (s.limit - s.pos); s = s.next) {
            offset -= (s.limit - s.pos);
        }

        // Copy one segment at a time.
        for (; byteCount > 0; s = s.next) {
            Segment copy = new Segment(s);
            copy.pos += offset;
            copy.limit = Math.min(copy.pos + (int) byteCount, copy.limit);
            if (out.head == null) {
                out.head = copy.next = copy.prev = copy;
            } else {
                out.head.prev.push(copy);
            }
            byteCount -= copy.limit - copy.pos;
            offset = 0;
        }

        return this;
    }

    /** Write the contents of this to {@code out}. */
    public Buffer writeTo(OutputStream out) throws IOException {
        return writeTo(out, size);
    }

    /** Write {@code byteCount} bytes from this to {@code out}. */
    public Buffer writeTo(OutputStream out, long byteCount) throws IOException {
        if (out == null) throw new IllegalArgumentException("out == null");
        checkOffsetAndCount(size, 0, byteCount);

        Segment s = head;
        while (byteCount > 0) {
            int toCopy = (int) Math.min(byteCount, s.limit - s.pos);
            out.write(s.data, s.pos, toCopy);

            s.pos += toCopy;
            size -= toCopy;
            byteCount -= toCopy;

            if (s.pos == s.limit) {
                Segment toRecycle = s;
                head = s = toRecycle.pop();
                SegmentPool.recycle(toRecycle);
            }
        }

        return this;
    }

    /** Read and exhaust bytes from {@code in} to this. */
    public Buffer readFrom(InputStream in) throws IOException {
        readFrom(in, Long.MAX_VALUE, true);
        return this;
    }

    /** Read {@code byteCount} bytes from {@code in} to this. */
    public Buffer readFrom(InputStream in, long byteCount) throws IOException {
        if (byteCount < 0) throw new IllegalArgumentException("byteCount < 0: " + byteCount);
        readFrom(in, byteCount, false);
        return this;
    }

    private void readFrom(InputStream in, long byteCount, boolean forever) throws IOException {
        if (in == null) throw new IllegalArgumentException("in == null");
        while (byteCount > 0 || forever) {
            Segment tail = writableSegment(1);
            int maxToCopy = (int) Math.min(byteCount, Segment.SIZE - tail.limit);
            int bytesRead = in.read(tail.data, tail.limit, maxToCopy);
            if (bytesRead == -1) {
                if (forever) return;
                throw new EOFException();
            }
            tail.limit += bytesRead;
            size += bytesRead;
            byteCount -= bytesRead;
        }
    }

    /**
     * Returns the number of bytes in segments that are not writable. This is the
     * number of bytes that can be flushed immediately to an underlying sink
     * without harming throughput.
     */
    public long completeSegmentByteCount() {
        long result = size;
        if (result == 0) return 0;

        // Omit the tail if it's still writable.
        Segment tail = head.prev;
        if (tail.limit < Segment.SIZE && tail.owner) {
            result -= tail.limit - tail.pos;
        }

        return result;
    }

    @Override public byte readByte() {
        if (size == 0) throw new IllegalStateException("size == 0");

        Segment segment = head;
        int pos = segment.pos;
        int limit = segment.limit;

        byte[] data = segment.data;
        byte b = data[pos++];
        size -= 1;

        if (pos == limit) {
            head = segment.pop();
            SegmentPool.recycle(segment);
        } else {
            segment.pos = pos;
        }

        return b;
    }

    /** Returns the byte at {@code pos}. */
    public byte getByte(long pos) {
        checkOffsetAndCount(size, pos, 1);
        for (Segment s = head; true; s = s.next) {
            int segmentByteCount = s.limit - s.pos;
            if (pos < segmentByteCount) return s.data[s.pos + (int) pos];
            pos -= segmentByteCount;
        }
    }

    @Override public short readShort() {
        if (size < 2) throw new IllegalStateException("size < 2: " + size);

        Segment segment = head;
        int pos = segment.pos;
        int limit = segment.limit;

        // If the short is split across multiple segments, delegate to readByte().
        if (limit - pos < 2) {
            int s = (readByte() & 0xff) << 8
                    |   (readByte() & 0xff);
            return (short) s;
        }

        byte[] data = segment.data;
        int s = (data[pos++] & 0xff) << 8
                |   (data[pos++] & 0xff);
        size -= 2;

        if (pos == limit) {
            head = segment.pop();
            SegmentPool.recycle(segment);
        } else {
            segment.pos = pos;
        }

        return (short) s;
    }

    @Override public int readInt() {
        if (size < 4) throw new IllegalStateException("size < 4: " + size);

        Segment segment = head;
        int pos = segment.pos;
        int limit = segment.limit;

        // If the int is split across multiple segments, delegate to readByte().
        if (limit - pos < 4) {
            return (readByte() & 0xff) << 24
                    |  (readByte() & 0xff) << 16
                    |  (readByte() & 0xff) <<  8
                    |  (readByte() & 0xff);
        }

        byte[] data = segment.data;
        int i = (data[pos++] & 0xff) << 24
                |   (data[pos++] & 0xff) << 16
                |   (data[pos++] & 0xff) <<  8
                |   (data[pos++] & 0xff);
        size -= 4;

        if (pos == limit) {
            head = segment.pop();
            SegmentPool.recycle(segment);
        } else {
            segment.pos = pos;
        }

        return i;
    }

    @Override public long readLong() {
        if (size < 8) throw new IllegalStateException("size < 8: " + size);

        Segment segment = head;
        int pos = segment.pos;
        int limit = segment.limit;

        // If the long is split across multiple segments, delegate to readInt().
        if (limit - pos < 8) {
            return (readInt() & 0xffffffffL) << 32
                    |  (readInt() & 0xffffffffL);
        }

        byte[] data = segment.data;
        long v = (data[pos++] & 0xffL) << 56
                |    (data[pos++] & 0xffL) << 48
                |    (data[pos++] & 0xffL) << 40
                |    (data[pos++] & 0xffL) << 32
                |    (data[pos++] & 0xffL) << 24
                |    (data[pos++] & 0xffL) << 16
                |    (data[pos++] & 0xffL) <<  8
                |    (data[pos++] & 0xffL);
        size -= 8;

        if (pos == limit) {
            head = segment.pop();
            SegmentPool.recycle(segment);
        } else {
            segment.pos = pos;
        }

        return v;
    }

    @Override public short readShortLe() {
        return Util.reverseBytesShort(readShort());
    }

    @Override public int readIntLe() {
        return Util.reverseBytesInt(readInt());
    }

    @Override public long readLongLe() {
        return reverseBytesLong(readLong());
    }

    @Override public long readDecimalLong() {
        if (size == 0) throw new IllegalStateException("size == 0");

        // This value is always built negatively in order to accommodate Long.MIN_VALUE.
        long value = 0;
        int seen = 0;
        boolean negative = false;
        boolean done = false;

        long overflowZone = Long.MIN_VALUE / 10;
        long overflowDigit = (Long.MIN_VALUE % 10) + 1;

        do {
            Segment segment = head;

            byte[] data = segment.data;
            int pos = segment.pos;
            int limit = segment.limit;

            for (; pos < limit; pos++, seen++) {
                byte b = data[pos];
                if (b >= '0' && b <= '9') {
                    int digit = '0' - b;

                    // Detect when the digit would cause an overflow.
                    if (value < overflowZone || value == overflowZone && digit < overflowDigit) {
                        Buffer buffer = new Buffer().writeDecimalLong(value).writeByte(b);
                        if (!negative) buffer.readByte(); // Skip negative sign.
                        throw new NumberFormatException("Number too large: " + buffer.readUtf8());
                    }
                    value *= 10;
                    value += digit;
                } else if (b == '-' && seen == 0) {
                    negative = true;
                    overflowDigit -= 1;
                } else {
                    if (seen == 0) {
                        throw new NumberFormatException(
                                "Expected leading [0-9] or '-' character but was 0x" + Integer.toHexString(b));
                    }
                    // Set a flag to stop iteration. We still need to run through segment updating below.
                    done = true;
                    break;
                }
            }

            if (pos == limit) {
                head = segment.pop();
                SegmentPool.recycle(segment);
            } else {
                segment.pos = pos;
            }
        } while (!done && head != null);

        size -= seen;
        return negative ? value : -value;
    }

    @Override public long readHexadecimalUnsignedLong() {
        if (size == 0) throw new IllegalStateException("size == 0");

        long value = 0;
        int seen = 0;
        boolean done = false;

        do {
            Segment segment = head;

            byte[] data = segment.data;
            int pos = segment.pos;
            int limit = segment.limit;

            for (; pos < limit; pos++, seen++) {
                int digit;

                byte b = data[pos];
                if (b >= '0' && b <= '9') {
                    digit = b - '0';
                } else if (b >= 'a' && b <= 'f') {
                    digit = b - 'a' + 10;
                } else if (b >= 'A' && b <= 'F') {
                    digit = b - 'A' + 10; // We never write uppercase, but we support reading it.
                } else {
                    if (seen == 0) {
                        throw new NumberFormatException(
                                "Expected leading [0-9a-fA-F] character but was 0x" + Integer.toHexString(b));
                    }
                    // Set a flag to stop iteration. We still need to run through segment updating below.
                    done = true;
                    break;
                }

                // Detect when the shift will overflow.
                if ((value & 0xf000000000000000L) != 0) {
                    Buffer buffer = new Buffer().writeHexadecimalUnsignedLong(value).writeByte(b);
                    throw new NumberFormatException("Number too large: " + buffer.readUtf8());
                }

                value <<= 4;
                value |= digit;
            }

            if (pos == limit) {
                head = segment.pop();
                SegmentPool.recycle(segment);
            } else {
                segment.pos = pos;
            }
        } while (!done && head != null);

        size -= seen;
        return value;
    }

    @Override public ByteString readByteString() {
        return new ByteString(readByteArray());
    }

    @Override public ByteString readByteString(long byteCount) throws EOFException {
        return new ByteString(readByteArray(byteCount));
    }

    @Override public int select(Options options) {
        Segment s = head;
        if (s == null) return options.indexOf(ByteString.EMPTY);

        ByteString[] byteStrings = options.byteStrings;
        for (int i = 0, listSize = byteStrings.length; i < listSize; i++) {
            ByteString b = byteStrings[i];
            if (size >= b.size() && rangeEquals(s, s.pos, b, 0, b.size())) {
                try {
                    skip(b.size());
                    return i;
                } catch (EOFException e) {
                    throw new AssertionError(e);
                }
            }
        }
        return -1;
    }

    /**
     * Returns the index of a value in {@code options} that is either the prefix of this buffer, or
     * that this buffer is a prefix of. Unlike {@link #select} this never consumes the value, even
     * if it is found in full.
     */
    int selectPrefix(Options options) {
        Segment s = head;
        ByteString[] byteStrings = options.byteStrings;
        for (int i = 0, listSize = byteStrings.length; i < listSize; i++) {
            ByteString b = byteStrings[i];
            int bytesLimit = (int) Math.min(size, b.size());
            if (bytesLimit == 0 || rangeEquals(s, s.pos, b, 0, bytesLimit)) {
                return i;
            }
        }
        return -1;
    }

    @Override public void readFully(Buffer sink, long byteCount) throws EOFException {
        if (size < byteCount) {
            sink.write(this, size); // Exhaust ourselves.
            throw new EOFException();
        }
        sink.write(this, byteCount);
    }

    @Override public long readAll(Sink sink) throws IOException {
        long byteCount = size;
        if (byteCount > 0) {
            sink.write(this, byteCount);
        }
        return byteCount;
    }

    @Override public String readUtf8() {
        try {
            return readString(size, Util.UTF_8);
        } catch (EOFException e) {
            throw new AssertionError(e);
        }
    }

    @Override public String readUtf8(long byteCount) throws EOFException {
        return readString(byteCount, Util.UTF_8);
    }

    @Override public String readString(Charset charset) {
        try {
            return readString(size, charset);
        } catch (EOFException e) {
            throw new AssertionError(e);
        }
    }

    @Override public String readString(long byteCount, Charset charset) throws EOFException {
        checkOffsetAndCount(size, 0, byteCount);
        if (charset == null) throw new IllegalArgumentException("charset == null");
        if (byteCount > Integer.MAX_VALUE) {
            throw new IllegalArgumentException("byteCount > Integer.MAX_VALUE: " + byteCount);
        }
        if (byteCount == 0) return "";

        Segment s = head;
        if (s.pos + byteCount > s.limit) {
            // If the string spans multiple segments, delegate to readBytes().
            return new String(readByteArray(byteCount), charset);
        }

        String result = new String(s.data, s.pos, (int) byteCount, charset);
        s.pos += byteCount;
        size -= byteCount;

        if (s.pos == s.limit) {
            head = s.pop();
            SegmentPool.recycle(s);
        }

        return result;
    }

    @Override public String readUtf8Line() throws EOFException {
        long newline = indexOf((byte) '\n');

        if (newline == -1) {
            return size != 0 ? readUtf8(size) : null;
        }

        return readUtf8Line(newline);
    }

    @Override public String readUtf8LineStrict() throws EOFException {
        long newline = indexOf((byte) '\n');
        if (newline == -1) {
            Buffer data = new Buffer();
            copyTo(data, 0, Math.min(32, size));
            throw new EOFException("\\n not found: size=" + size()
                    + " content=" + data.readByteString().hex() + "…");
        }
        return readUtf8Line(newline);
    }

    String readUtf8Line(long newline) throws EOFException {
        if (newline > 0 && getByte(newline - 1) == '\r') {
            // Read everything until '\r\n', then skip the '\r\n'.
            String result = readUtf8((newline - 1));
            skip(2);
            return result;

        } else {
            // Read everything until '\n', then skip the '\n'.
            String result = readUtf8(newline);
            skip(1);
            return result;
        }
    }

    @Override public int readUtf8CodePoint() throws EOFException {
        if (size == 0) throw new EOFException();

        byte b0 = getByte(0);
        int codePoint;
        int byteCount;
        int min;

        if ((b0 & 0x80) == 0) {
            // 0xxxxxxx.
            codePoint = b0 & 0x7f;
            byteCount = 1; // 7 bits (ASCII).
            min = 0x0;

        } else if ((b0 & 0xe0) == 0xc0) {
            // 0x110xxxxx
            codePoint = b0 & 0x1f;
            byteCount = 2; // 11 bits (5 + 6).
            min = 0x80;

        } else if ((b0 & 0xf0) == 0xe0) {
            // 0x1110xxxx
            codePoint = b0 & 0x0f;
            byteCount = 3; // 16 bits (4 + 6 + 6).
            min = 0x800;

        } else if ((b0 & 0xf8) == 0xf0) {
            // 0x11110xxx
            codePoint = b0 & 0x07;
            byteCount = 4; // 21 bits (3 + 6 + 6 + 6).
            min = 0x10000;

        } else {
            // We expected the first byte of a code point but got something else.
            skip(1);
            return REPLACEMENT_CHARACTER;
        }

        if (size < byteCount) {
            throw new EOFException("size < " + byteCount + ": " + size
                    + " (to read code point prefixed 0x" + Integer.toHexString(b0) + ")");
        }

        // Read the continuation bytes. If we encounter a non-continuation byte, the sequence consumed
        // thus far is truncated and is decoded as the replacement character. That non-continuation byte
        // is left in the stream for processing by the next call to readUtf8CodePoint().
        for (int i = 1; i < byteCount; i++) {
            byte b = getByte(i);
            if ((b & 0xc0) == 0x80) {
                // 0x10xxxxxx
                codePoint <<= 6;
                codePoint |= b & 0x3f;
            } else {
                skip(i);
                return REPLACEMENT_CHARACTER;
            }
        }

        skip(byteCount);

        if (codePoint > 0x10ffff) {
            return REPLACEMENT_CHARACTER; // Reject code points larger than the Unicode maximum.
        }

        if (codePoint >= 0xd800 && codePoint <= 0xdfff) {
            return REPLACEMENT_CHARACTER; // Reject partial surrogates.
        }

        if (codePoint < min) {
            return REPLACEMENT_CHARACTER; // Reject overlong code points.
        }

        return codePoint;
    }

    @Override public byte[] readByteArray() {
        try {
            return readByteArray(size);
        } catch (EOFException e) {
            throw new AssertionError(e);
        }
    }

    @Override public byte[] readByteArray(long byteCount) throws EOFException {
        checkOffsetAndCount(size, 0, byteCount);
        if (byteCount > Integer.MAX_VALUE) {
            throw new IllegalArgumentException("byteCount > Integer.MAX_VALUE: " + byteCount);
        }

        byte[] result = new byte[(int) byteCount];
        readFully(result);
        return result;
    }

    @Override public int read(byte[] sink) {
        return read(sink, 0, sink.length);
    }

    @Override public void readFully(byte[] sink) throws EOFException {
        int offset = 0;
        while (offset < sink.length) {
            int read = read(sink, offset, sink.length - offset);
            if (read == -1) throw new EOFException();
            offset += read;
        }
    }

    @Override public int read(byte[] sink, int offset, int byteCount) {
        checkOffsetAndCount(sink.length, offset, byteCount);

        Segment s = head;
        if (s == null) return -1;
        int toCopy = Math.min(byteCount, s.limit - s.pos);
        System.arraycopy(s.data, s.pos, sink, offset, toCopy);

        s.pos += toCopy;
        size -= toCopy;

        if (s.pos == s.limit) {
            head = s.pop();
            SegmentPool.recycle(s);
        }

        return toCopy;
    }

    /**
     * Discards all bytes in this buffer. Calling this method when you're done
     * with a buffer will return its segments to the pool.
     */
    public void clear() {
        try {
            skip(size);
        } catch (EOFException e) {
            throw new AssertionError(e);
        }
    }

    /** Discards {@code byteCount} bytes from the head of this buffer. */
    @Override public void skip(long byteCount) throws EOFException {
        while (byteCount > 0) {
            if (head == null) throw new EOFException();

            int toSkip = (int) Math.min(byteCount, head.limit - head.pos);
            size -= toSkip;
            byteCount -= toSkip;
            head.pos += toSkip;

            if (head.pos == head.limit) {
                Segment toRecycle = head;
                head = toRecycle.pop();
                SegmentPool.recycle(toRecycle);
            }
        }
    }

    @Override public Buffer write(ByteString byteString) {
        if (byteString == null) throw new IllegalArgumentException("byteString == null");
        byteString.write(this);
        return this;
    }

    @Override public Buffer writeUtf8(String string) {
        return writeUtf8(string, 0, string.length());
    }

    @Override public Buffer writeUtf8(String string, int beginIndex, int endIndex) {
        if (string == null) throw new IllegalArgumentException("string == null");
        if (beginIndex < 0) throw new IllegalAccessError("beginIndex < 0: " + beginIndex);
        if (endIndex < beginIndex) {
            throw new IllegalArgumentException("endIndex < beginIndex: " + endIndex + " < " + beginIndex);
        }
        if (endIndex > string.length()) {
            throw new IllegalArgumentException(
                    "endIndex > string.length: " + endIndex + " > " + string.length());
        }

        // Transcode a UTF-16 Java String to UTF-8 bytes.
        for (int i = beginIndex; i < endIndex;) {
            int c = string.charAt(i);

            if (c < 0x80) {
                Segment tail = writableSegment(1);
                byte[] data = tail.data;
                int segmentOffset = tail.limit - i;
                int runLimit = Math.min(endIndex, Segment.SIZE - segmentOffset);

                // Emit a 7-bit character with 1 byte.
                data[segmentOffset + i++] = (byte) c; // 0xxxxxxx

                // Fast-path contiguous runs of ASCII characters. This is ugly, but yields a ~4x performance
                // improvement over independent calls to writeByte().
                while (i < runLimit) {
                    c = string.charAt(i);
                    if (c >= 0x80) break;
                    data[segmentOffset + i++] = (byte) c; // 0xxxxxxx
                }

                int runSize = i + segmentOffset - tail.limit; // Equivalent to i - (previous i).
                tail.limit += runSize;
                size += runSize;

            } else if (c < 0x800) {
                // Emit a 11-bit character with 2 bytes.
                writeByte(c >>  6        | 0xc0); // 110xxxxx
                writeByte(c       & 0x3f | 0x80); // 10xxxxxx
                i++;

            } else if (c < 0xd800 || c > 0xdfff) {
                // Emit a 16-bit character with 3 bytes.
                writeByte(c >> 12        | 0xe0); // 1110xxxx
                writeByte(c >>  6 & 0x3f | 0x80); // 10xxxxxx
                writeByte(c       & 0x3f | 0x80); // 10xxxxxx
                i++;

            } else {
                // c is a surrogate. Make sure it is a high surrogate & that its successor is a low
                // surrogate. If not, the UTF-16 is invalid, in which case we emit a replacement character.
                int low = i + 1 < endIndex ? string.charAt(i + 1) : 0;
                if (c > 0xdbff || low < 0xdc00 || low > 0xdfff) {
                    writeByte('?');
                    i++;
                    continue;
                }

                // UTF-16 high surrogate: 110110xxxxxxxxxx (10 bits)
                // UTF-16 low surrogate:  110111yyyyyyyyyy (10 bits)
                // Unicode code point:    00010000000000000000 + xxxxxxxxxxyyyyyyyyyy (21 bits)
                int codePoint = 0x010000 + ((c & ~0xd800) << 10 | low & ~0xdc00);

                // Emit a 21-bit character with 4 bytes.
                writeByte(codePoint >> 18        | 0xf0); // 11110xxx
                writeByte(codePoint >> 12 & 0x3f | 0x80); // 10xxxxxx
                writeByte(codePoint >>  6 & 0x3f | 0x80); // 10xxyyyy
                writeByte(codePoint       & 0x3f | 0x80); // 10yyyyyy
                i += 2;
            }
        }

        return this;
    }

    @Override public Buffer writeUtf8CodePoint(int codePoint) {
        if (codePoint < 0x80) {
            // Emit a 7-bit code point with 1 byte.
            writeByte(codePoint);

        } else if (codePoint < 0x800) {
            // Emit a 11-bit code point with 2 bytes.
            writeByte(codePoint >>  6        | 0xc0); // 110xxxxx
            writeByte(codePoint       & 0x3f | 0x80); // 10xxxxxx

        } else if (codePoint < 0x10000) {
            if (codePoint >= 0xd800 && codePoint <= 0xdfff) {
                throw new IllegalArgumentException(
                        "Unexpected code point: " + Integer.toHexString(codePoint));
            }

            // Emit a 16-bit code point with 3 bytes.
            writeByte(codePoint >> 12        | 0xe0); // 1110xxxx
            writeByte(codePoint >>  6 & 0x3f | 0x80); // 10xxxxxx
            writeByte(codePoint       & 0x3f | 0x80); // 10xxxxxx

        } else if (codePoint <= 0x10ffff) {
            // Emit a 21-bit code point with 4 bytes.
            writeByte(codePoint >> 18        | 0xf0); // 11110xxx
            writeByte(codePoint >> 12 & 0x3f | 0x80); // 10xxxxxx
            writeByte(codePoint >>  6 & 0x3f | 0x80); // 10xxxxxx
            writeByte(codePoint       & 0x3f | 0x80); // 10xxxxxx

        } else {
            throw new IllegalArgumentException(
                    "Unexpected code point: " + Integer.toHexString(codePoint));
        }

        return this;
    }

    @Override public Buffer writeString(String string, Charset charset) {
        return writeString(string, 0, string.length(), charset);
    }

    @Override
    public Buffer writeString(String string, int beginIndex, int endIndex, Charset charset) {
        if (string == null) throw new IllegalArgumentException("string == null");
        if (beginIndex < 0) throw new IllegalAccessError("beginIndex < 0: " + beginIndex);
        if (endIndex < beginIndex) {
            throw new IllegalArgumentException("endIndex < beginIndex: " + endIndex + " < " + beginIndex);
        }
        if (endIndex > string.length()) {
            throw new IllegalArgumentException(
                    "endIndex > string.length: " + endIndex + " > " + string.length());
        }
        if (charset == null) throw new IllegalArgumentException("charset == null");
        if (charset.equals(Util.UTF_8)) return writeUtf8(string);
        byte[] data = string.substring(beginIndex, endIndex).getBytes(charset);
        return write(data, 0, data.length);
    }

    @Override public Buffer write(byte[] source) {
        if (source == null) throw new IllegalArgumentException("source == null");
        return write(source, 0, source.length);
    }

    @Override public Buffer write(byte[] source, int offset, int byteCount) {
        if (source == null) throw new IllegalArgumentException("source == null");
        checkOffsetAndCount(source.length, offset, byteCount);

        int limit = offset + byteCount;
        while (offset < limit) {
            Segment tail = writableSegment(1);

            int toCopy = Math.min(limit - offset, Segment.SIZE - tail.limit);
            System.arraycopy(source, offset, tail.data, tail.limit, toCopy);

            offset += toCopy;
            tail.limit += toCopy;
        }

        size += byteCount;
        return this;
    }

    @Override public long writeAll(Source source) throws IOException {
        if (source == null) throw new IllegalArgumentException("source == null");
        long totalBytesRead = 0;
        for (long readCount; (readCount = source.read(this, Segment.SIZE)) != -1; ) {
            totalBytesRead += readCount;
        }
        return totalBytesRead;
    }

    @Override public BufferedSink write(Source source, long byteCount) throws IOException {
        while (byteCount > 0) {
            long read = source.read(this, byteCount);
            if (read == -1) throw new EOFException();
            byteCount -= read;
        }
        return this;
    }

    @Override public Buffer writeByte(int b) {
        Segment tail = writableSegment(1);
        tail.data[tail.limit++] = (byte) b;
        size += 1;
        return this;
    }

    @Override public Buffer writeShort(int s) {
        Segment tail = writableSegment(2);
        byte[] data = tail.data;
        int limit = tail.limit;
        data[limit++] = (byte) ((s >>> 8) & 0xff);
        data[limit++] = (byte)  (s        & 0xff);
        tail.limit = limit;
        size += 2;
        return this;
    }

    @Override public Buffer writeShortLe(int s) {
        return writeShort(Util.reverseBytesShort((short) s));
    }

    @Override public Buffer writeInt(int i) {
        Segment tail = writableSegment(4);
        byte[] data = tail.data;
        int limit = tail.limit;
        data[limit++] = (byte) ((i >>> 24) & 0xff);
        data[limit++] = (byte) ((i >>> 16) & 0xff);
        data[limit++] = (byte) ((i >>>  8) & 0xff);
        data[limit++] = (byte)  (i         & 0xff);
        tail.limit = limit;
        size += 4;
        return this;
    }

    @Override public Buffer writeIntLe(int i) {
        return writeInt(Util.reverseBytesInt(i));
    }

    @Override public Buffer writeLong(long v) {
        Segment tail = writableSegment(8);
        byte[] data = tail.data;
        int limit = tail.limit;
        data[limit++] = (byte) ((v >>> 56L) & 0xff);
        data[limit++] = (byte) ((v >>> 48L) & 0xff);
        data[limit++] = (byte) ((v >>> 40L) & 0xff);
        data[limit++] = (byte) ((v >>> 32L) & 0xff);
        data[limit++] = (byte) ((v >>> 24L) & 0xff);
        data[limit++] = (byte) ((v >>> 16L) & 0xff);
        data[limit++] = (byte) ((v >>>  8L) & 0xff);
        data[limit++] = (byte)  (v          & 0xff);
        tail.limit = limit;
        size += 8;
        return this;
    }

    @Override public Buffer writeLongLe(long v) {
        return writeLong(reverseBytesLong(v));
    }

    @Override public Buffer writeDecimalLong(long v) {
        if (v == 0) {
            // Both a shortcut and required since the following code can't handle zero.
            return writeByte('0');
        }

        boolean negative = false;
        if (v < 0) {
            v = -v;
            if (v < 0) { // Only true for Long.MIN_VALUE.
                return writeUtf8("-9223372036854775808");
            }
            negative = true;
        }

        // Binary search for character width which favors matching lower numbers.
        int width = //
                v < 100000000L
                        ? v < 10000L
                        ? v < 100L
                        ? v < 10L ? 1 : 2
                        : v < 1000L ? 3 : 4
                        : v < 1000000L
                        ? v < 100000L ? 5 : 6
                        : v < 10000000L ? 7 : 8
                        : v < 1000000000000L
                        ? v < 10000000000L
                        ? v < 1000000000L ? 9 : 10
                        : v < 100000000000L ? 11 : 12
                        : v < 1000000000000000L
                        ? v < 10000000000000L ? 13
                        : v < 100000000000000L ? 14 : 15
                        : v < 100000000000000000L
                        ? v < 10000000000000000L ? 16 : 17
                        : v < 1000000000000000000L ? 18 : 19;
        if (negative) {
            ++width;
        }

        Segment tail = writableSegment(width);
        byte[] data = tail.data;
        int pos = tail.limit + width; // We write backwards from right to left.
        while (v != 0) {
            int digit = (int) (v % 10);
            data[--pos] = DIGITS[digit];
            v /= 10;
        }
        if (negative) {
            data[--pos] = '-';
        }

        tail.limit += width;
        this.size += width;
        return this;
    }

    @Override public Buffer writeHexadecimalUnsignedLong(long v) {
        if (v == 0) {
            // Both a shortcut and required since the following code can't handle zero.
            return writeByte('0');
        }

        int width = Long.numberOfTrailingZeros(Long.highestOneBit(v)) / 4 + 1;

        Segment tail = writableSegment(width);
        byte[] data = tail.data;
        for (int pos = tail.limit + width - 1, start = tail.limit; pos >= start; pos--) {
            data[pos] = DIGITS[(int) (v & 0xF)];
            v >>>= 4;
        }
        tail.limit += width;
        size += width;
        return this;
    }

    /**
     * Returns a tail segment that we can write at least {@code minimumCapacity}
     * bytes to, creating it if necessary.
     */
    Segment writableSegment(int minimumCapacity) {
        if (minimumCapacity < 1 || minimumCapacity > Segment.SIZE) throw new IllegalArgumentException();

        if (head == null) {
            head = SegmentPool.take(); // Acquire a first segment.
            return head.next = head.prev = head;
        }

        Segment tail = head.prev;
        if (tail.limit + minimumCapacity > Segment.SIZE || !tail.owner) {
            tail = tail.push(SegmentPool.take()); // Append a new empty segment to fill up.
        }
        return tail;
    }

    @Override public void write(Buffer source, long byteCount) {
        // Move bytes from the head of the source buffer to the tail of this buffer
        // while balancing two conflicting goals: don't waste CPU and don't waste
        // memory.
        //
        //
        // Don't waste CPU (ie. don't copy data around).
        //
        // Copying large amounts of data is expensive. Instead, we prefer to
        // reassign entire segments from one buffer to the other.
        //
        //
        // Don't waste memory.
        //
        // As an invariant, adjacent pairs of segments in a buffer should be at
        // least 50% full, except for the head segment and the tail segment.
        //
        // The head segment cannot maintain the invariant because the application is
        // consuming bytes from this segment, decreasing its level.
        //
        // The tail segment cannot maintain the invariant because the application is
        // producing bytes, which may require new nearly-empty tail segments to be
        // appended.
        //
        //
        // Moving segments between buffers
        //
        // When writing one buffer to another, we prefer to reassign entire segments
        // over copying bytes into their most compact form. Suppose we have a buffer
        // with these segment levels [91%, 61%]. If we append a buffer with a
        // single [72%] segment, that yields [91%, 61%, 72%]. No bytes are copied.
        //
        // Or suppose we have a buffer with these segment levels: [100%, 2%], and we
        // want to append it to a buffer with these segment levels [99%, 3%]. This
        // operation will yield the following segments: [100%, 2%, 99%, 3%]. That
        // is, we do not spend time copying bytes around to achieve more efficient
        // memory use like [100%, 100%, 4%].
        //
        // When combining buffers, we will compact adjacent buffers when their
        // combined level doesn't exceed 100%. For example, when we start with
        // [100%, 40%] and append [30%, 80%], the result is [100%, 70%, 80%].
        //
        //
        // Splitting segments
        //
        // Occasionally we write only part of a source buffer to a sink buffer. For
        // example, given a sink [51%, 91%], we may want to write the first 30% of
        // a source [92%, 82%] to it. To simplify, we first transform the source to
        // an equivalent buffer [30%, 62%, 82%] and then move the head segment,
        // yielding sink [51%, 91%, 30%] and source [62%, 82%].

        if (source == null) throw new IllegalArgumentException("source == null");
        if (source == this) throw new IllegalArgumentException("source == this");
        checkOffsetAndCount(source.size, 0, byteCount);

        while (byteCount > 0) {
            // Is a prefix of the source's head segment all that we need to move?
            if (byteCount < (source.head.limit - source.head.pos)) {
                Segment tail = head != null ? head.prev : null;
                if (tail != null && tail.owner
                        && (byteCount + tail.limit - (tail.shared ? 0 : tail.pos) <= Segment.SIZE)) {
                    // Our existing segments are sufficient. Move bytes from source's head to our tail.
                    source.head.writeTo(tail, (int) byteCount);
                    source.size -= byteCount;
                    size += byteCount;
                    return;
                } else {
                    // We're going to need another segment. Split the source's head
                    // segment in two, then move the first of those two to this buffer.
                    source.head = source.head.split((int) byteCount);
                }
            }

            // Remove the source's head segment and append it to our tail.
            Segment segmentToMove = source.head;
            long movedByteCount = segmentToMove.limit - segmentToMove.pos;
            source.head = segmentToMove.pop();
            if (head == null) {
                head = segmentToMove;
                head.next = head.prev = head;
            } else {
                Segment tail = head.prev;
                tail = tail.push(segmentToMove);
                tail.compact();
            }
            source.size -= movedByteCount;
            size += movedByteCount;
            byteCount -= movedByteCount;
        }
    }

    @Override public long read(Buffer sink, long byteCount) {
        if (sink == null) throw new IllegalArgumentException("sink == null");
        if (byteCount < 0) throw new IllegalArgumentException("byteCount < 0: " + byteCount);
        if (size == 0) return -1L;
        if (byteCount > size) byteCount = size;
        sink.write(this, byteCount);
        return byteCount;
    }

    @Override public long indexOf(byte b) {
        return indexOf(b, 0);
    }

    /**
     * Returns the index of {@code b} in this at or beyond {@code fromIndex}, or
     * -1 if this buffer does not contain {@code b} in that range.
     */
    @Override public long indexOf(byte b, long fromIndex) {
        if (fromIndex < 0) throw new IllegalArgumentException("fromIndex < 0");

        Segment s;
        long offset;

        // TODO(jwilson): extract this to a shared helper method when can do so without allocating.
        findSegmentAndOffset: {
            // Pick the first segment to scan. This is the first segment with offset <= fromIndex.
            s = head;
            if (s == null) {
                // No segments to scan!
                return -1L;
            } else if (size - fromIndex < fromIndex) {
                // We're scanning in the back half of this buffer. Find the segment starting at the back.
                offset = size;
                while (offset > fromIndex) {
                    s = s.prev;
                    offset -= (s.limit - s.pos);
                }
            } else {
                // We're scanning in the front half of this buffer. Find the segment starting at the front.
                offset = 0L;
                for (long nextOffset; (nextOffset = offset + (s.limit - s.pos)) < fromIndex; ) {
                    s = s.next;
                    offset = nextOffset;
                }
            }
        }

        // Scan through the segments, searching for b.
        while (offset < size) {
            byte[] data = s.data;
            for (int pos = (int) (s.pos + fromIndex - offset), limit = s.limit; pos < limit; pos++) {
                if (data[pos] == b) {
                    return pos - s.pos + offset;
                }
            }

            // Not in this segment. Try the next one.
            offset += (s.limit - s.pos);
            fromIndex = offset;
            s = s.next;
        }

        return -1L;
    }

    @Override public long indexOf(ByteString bytes) throws IOException {
        return indexOf(bytes, 0);
    }

    @Override public long indexOf(ByteString bytes, long fromIndex) throws IOException {
        if (bytes.size() == 0) throw new IllegalArgumentException("bytes is empty");
        if (fromIndex < 0) throw new IllegalArgumentException("fromIndex < 0");

        Segment s;
        long offset;

        // TODO(jwilson): extract this to a shared helper method when can do so without allocating.
        findSegmentAndOffset: {
            // Pick the first segment to scan. This is the first segment with offset <= fromIndex.
            s = head;
            if (s == null) {
                // No segments to scan!
                return -1L;
            } else if (size - fromIndex < fromIndex) {
                // We're scanning in the back half of this buffer. Find the segment starting at the back.
                offset = size;
                while (offset > fromIndex) {
                    s = s.prev;
                    offset -= (s.limit - s.pos);
                }
            } else {
                // We're scanning in the front half of this buffer. Find the segment starting at the front.
                offset = 0L;
                for (long nextOffset; (nextOffset = offset + (s.limit - s.pos)) < fromIndex; ) {
                    s = s.next;
                    offset = nextOffset;
                }
            }
        }

        // Scan through the segments, searching for the lead byte. Each time that is found, delegate to
        // rangeEquals() to check for a complete match.
        byte b0 = bytes.getByte(0);
        int bytesSize = bytes.size();
        long resultLimit = size - bytesSize + 1;
        while (offset < resultLimit) {
            // Scan through the current segment.
            byte[] data = s.data;
            int segmentLimit = (int) Math.min(s.limit, s.pos + resultLimit - offset);
            for (int pos = (int) (s.pos + fromIndex - offset); pos < segmentLimit; pos++) {
                if (data[pos] == b0 && rangeEquals(s, pos + 1, bytes, 1, bytesSize)) {
                    return pos - s.pos + offset;
                }
            }

            // Not in this segment. Try the next one.
            offset += (s.limit - s.pos);
            fromIndex = offset;
            s = s.next;
        }

        return -1L;
    }

    @Override public long indexOfElement(ByteString targetBytes) {
        return indexOfElement(targetBytes, 0);
    }

    @Override public long indexOfElement(ByteString targetBytes, long fromIndex) {
        if (fromIndex < 0) throw new IllegalArgumentException("fromIndex < 0");

        Segment s;
        long offset;

        // TODO(jwilson): extract this to a shared helper method when can do so without allocating.
        findSegmentAndOffset: {
            // Pick the first segment to scan. This is the first segment with offset <= fromIndex.
            s = head;
            if (s == null) {
                // No segments to scan!
                return -1L;
            } else if (size - fromIndex < fromIndex) {
                // We're scanning in the back half of this buffer. Find the segment starting at the back.
                offset = size;
                while (offset > fromIndex) {
                    s = s.prev;
                    offset -= (s.limit - s.pos);
                }
            } else {
                // We're scanning in the front half of this buffer. Find the segment starting at the front.
                offset = 0L;
                for (long nextOffset; (nextOffset = offset + (s.limit - s.pos)) < fromIndex; ) {
                    s = s.next;
                    offset = nextOffset;
                }
            }
        }

        // Special case searching for one of two bytes. This is a common case for tools like Moshi,
        // which search for pairs of chars like `\r` and `\n` or {@code `"` and `\`. The impact of this
        // optimization is a ~5x speedup for this case without a substantial cost to other cases.
        if (targetBytes.size() == 2) {
            // Scan through the segments, searching for either of the two bytes.
            byte b0 = targetBytes.getByte(0);
            byte b1 = targetBytes.getByte(1);
            while (offset < size) {
                byte[] data = s.data;
                for (int pos = (int) (s.pos + fromIndex - offset), limit = s.limit; pos < limit; pos++) {
                    int b = data[pos];
                    if (b == b0 || b == b1) {
                        return pos - s.pos + offset;
                    }
                }

                // Not in this segment. Try the next one.
                offset += (s.limit - s.pos);
                fromIndex = offset;
                s = s.next;
            }
        } else {
            // Scan through the segments, searching for a byte that's also in the array.
            byte[] targetByteArray = targetBytes.internalArray();
            while (offset < size) {
                byte[] data = s.data;
                for (int pos = (int) (s.pos + fromIndex - offset), limit = s.limit; pos < limit; pos++) {
                    int b = data[pos];
                    for (byte t : targetByteArray) {
                        if (b == t) return pos - s.pos + offset;
                    }
                }

                // Not in this segment. Try the next one.
                offset += (s.limit - s.pos);
                fromIndex = offset;
                s = s.next;
            }
        }

        return -1L;
    }

    @Override public boolean rangeEquals(long offset, ByteString bytes) {
        return rangeEquals(offset, bytes, 0, bytes.size());
    }

    @Override public boolean rangeEquals(long offset, ByteString bytes, int bytesOffset, int byteCount) {
        if (offset < 0
                || bytesOffset < 0
                || byteCount < 0
                || size - offset < byteCount
                || bytes.size() - bytesOffset < byteCount) {
            return false;
        }
        for (int i = 0; i < byteCount; i++) {
            if (getByte(offset + i) != bytes.getByte(bytesOffset + i)) {
                return false;
            }
        }
        return true;
    }

    /**
     * Returns true if the range within this buffer starting at {@code segmentPos} in {@code segment}
     * is equal to {@code bytes[bytesOffset..bytesLimit)}.
     */
    private boolean rangeEquals(
            Segment segment, int segmentPos, ByteString bytes, int bytesOffset, int bytesLimit) {
        int segmentLimit = segment.limit;
        byte[] data = segment.data;

        for (int i = bytesOffset; i < bytesLimit; ) {
            if (segmentPos == segmentLimit) {
                segment = segment.next;
                data = segment.data;
                segmentPos = segment.pos;
                segmentLimit = segment.limit;
            }

            if (data[segmentPos] != bytes.getByte(i)) {
                return false;
            }

            segmentPos++;
            i++;
        }

        return true;
    }

    @Override public void flush() {
    }

    @Override public void close() {
    }

    @Override public Timeout timeout() {
        return Timeout.NONE;
    }

    /** For testing. This returns the sizes of the segments in this buffer. */
    List<Integer> segmentSizes() {
        if (head == null) return Collections.emptyList();
        List<Integer> result = new ArrayList<>();
        result.add(head.limit - head.pos);
        for (Segment s = head.next; s != head; s = s.next) {
            result.add(s.limit - s.pos);
        }
        return result;
    }

    /** Returns the MD5 hash of this buffer. */
    public ByteString md5() {
        return digest("MD5");
    }

    /** Returns the SHA-1 hash of this buffer. */
    public ByteString sha1() {
        return digest("SHA-1");
    }

    /** Returns the SHA-256 hash of this buffer. */
    public ByteString sha256() {
        return digest("SHA-256");
    }

    private ByteString digest(String algorithm) {
        try {
            MessageDigest messageDigest = MessageDigest.getInstance(algorithm);
            messageDigest.update(head.data, head.pos, head.limit - head.pos);
            for (Segment s = head.next; s != head; s = s.next) {
                messageDigest.update(s.data, s.pos, s.limit - s.pos);
            }
            return ByteString.of(messageDigest.digest());
        } catch (NoSuchAlgorithmException e) {
            throw new AssertionError();
        }
    }

    @Override public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Buffer)) return false;
        Buffer that = (Buffer) o;
        if (size != that.size) return false;
        if (size == 0) return true; // Both buffers are empty.

        Segment sa = this.head;
        Segment sb = that.head;
        int posA = sa.pos;
        int posB = sb.pos;

        for (long pos = 0, count; pos < size; pos += count) {
            count = Math.min(sa.limit - posA, sb.limit - posB);

            for (int i = 0; i < count; i++) {
                if (sa.data[posA++] != sb.data[posB++]) return false;
            }

            if (posA == sa.limit) {
                sa = sa.next;
                posA = sa.pos;
            }

            if (posB == sb.limit) {
                sb = sb.next;
                posB = sb.pos;
            }
        }

        return true;
    }

    @Override public int hashCode() {
        Segment s = head;
        if (s == null) return 0;
        int result = 1;
        do {
            for (int pos = s.pos, limit = s.limit; pos < limit; pos++) {
                result = 31 * result + s.data[pos];
            }
            s = s.next;
        } while (s != head);
        return result;
    }

    /**
     * Returns a human-readable string that describes the contents of this buffer. Typically this
     * is a string like {@code [text=Hello]} or {@code [hex=0000ffff]}.
     */
    @Override public String toString() {
        return snapshot().toString();
    }

    /** Returns a deep copy of this buffer. */
    @Override public Buffer clone() {
        Buffer result = new Buffer();
        if (size == 0) return result;

        result.head = new Segment(head);
        result.head.next = result.head.prev = result.head;
        for (Segment s = head.next; s != head; s = s.next) {
            result.head.prev.push(new Segment(s));
        }
        result.size = size;
        return result;
    }

    /** Returns an immutable copy of this buffer as a byte string. */
    public ByteString snapshot() {
        if (size > Integer.MAX_VALUE) {
            throw new IllegalArgumentException("size > Integer.MAX_VALUE: " + size);
        }
        return snapshot((int) size);
    }

    /**
     * Returns an immutable copy of the first {@code byteCount} bytes of this buffer as a byte string.
     */
    public ByteString snapshot(int byteCount) {
        if (byteCount == 0) return ByteString.EMPTY;
        return new SegmentedByteString(this, byteCount);
    }
}
